The invention concerns a safety belt fastener, for receiving and latching an insertion tongue, having a housing and an insertion path for the insertion tongue, the insertion path being arranged in the housing and containing a spring-based ejector having a latch means guided in the fastener for cooperation with a recess in the tongue to achieve latching, the latch means then holding the insertion tongue in an associated recess of the fastener, and a spring-loaded shift key guided at right angles to the movement plane of the latch means for lifting the latch means, the movement of this shift key being composed of an unlatching stroke preceded by an idle stroke.
Safety belt fasteners generally have the particular problem that the latch opens automatically under extreme conditions, especially under the action of acceleration forces acting on the fastener in the individual case, if the operating parts of securing parts actuating the latch, or the latch itself, move out of their latching position due to their mass inertia and thus finally the latch is released from its latching position
A shift-key fastener of this type is known from DE-OS 28 28 049, in which the latch is moveable perpendicularly to the insertion tongue and which, when latched, is secured by a projection, arranged on the shift key travelling over the latch, against acceleration forces acting in the plane of the travel movement of the latch. However, acceleration forces can act on the fastener in the action plane of the shift key for actuating the latch, for example if the fastener is moved in its longitudinal direction as a result of a tightening of the safety belt when an accident occurs. If the housing of the fastener is suddenly stopped at the end of such tightening movement, the shift key continues to move in the tightening direction due to its mass inertia, with the result that the shift key and the fastener body experience a movement relative to one another during which the shift key is inserted into the fastener body and as a result carries out an opening movement to release the latch to effect unlatching.
In a safety belt fastener as described in DE-OS 35 33 684, securing of the shift key in the case of acceleration takes place through association of an additional mass which compensates for the acceleration forces and mass forces acting on the shift key. Such an additionally applied additional mass, however, is costly and causes a complicated fastener construction as well as a correspondingly complicated fastener mechanism when opening and closing the fastener.
The object underlying the invention therefore is to improve a shift-key fastener of the type named at the beginning in such a way that its anti-shock means against acceleration forces acting in the action direction of the shift key are simplified.